JPH0752620A - Wheel pneumatic pressure detector - Google Patents

Abstract

PURPOSE:To maintain proper detection accuracy even in mountainous region and city area where multistory buildings stand with respect to a wheel pneumatic pressure detector which assumes pneumatic pressure of each wheel based on whether rotating speed of the wheel relative to ground speed of a vehicle is proper or not. CONSTITUTION:Wheel speed sensors 19a-19d which detect rotating speed per wheel FW1, FW2, RW1, RW2 are provided. A ground car speed sensor 20 which generates wave having a predetermined frequency from a vehicle for a road surface, receives reflected wave which contains a Doppler shift which accompanies running of a vehicle, and detects fluctuation of frequency is mounted. A microcomputer 18 compares absolute car speed operated on the value detected by the ground car speed sensor 20 with wheel speed operated based on the value detected by the wheel speed sensors 19a-19d, and judges that pneumatic pressure is insufficient when wheel speed is high unreasonably and that pneumatic pressure is excessive when the speed is low unreasonably.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wheel air pressure detecting device, and more particularly, to detecting the ground vehicle speed of a vehicle as an absolute vehicle speed and determining the air pressure of each wheel depending on whether or not the rotation speed of each wheel is appropriate for the absolute vehicle speed. The present invention relates to an estimated wheel air pressure detection device.

[0002]

2. Description of the Related Art Conventionally, a global positioning system (GPS) is used to detect an absolute position of a vehicle, and an absolute vehicle speed of the vehicle is calculated from a temporal change thereof.
There is known a device that estimates the air pressure of a wheel based on whether or not the value of a wheel speed sensor installed for each wheel is an appropriate level for the absolute vehicle speed (Japanese Patent Laid-Open No. 2-106415).

That is, since the diameter of the wheel during traveling fluctuates due to the wheel air pressure, and the rotational speed of the wheel with respect to the absolute vehicle speed fluctuates due to the wheel air pressure. If the air pressure is insufficient, it is possible to judge that the air pressure is excessive.

Then, the above-mentioned device adopts a structure for detecting the absolute position of the vehicle by means of GPS as means for detecting the absolute vehicle speed which does not depend on the wheel condition and the like, and monitoring the time variation of the absolute position to estimate the absolute vehicle speed. It was done.

[0005]

However, the detection of the absolute position by the GPS sometimes becomes undetectable in an urban area where there are many high-rise buildings or in a mountainous area where tunnels are continuous. In this case, if the GPS is simply used as the position detection, there is no problem because the accurate absolute position can be detected immediately when the detection becomes possible, but the wheel air pressure is calculated based on the absolute position. There is a problem when trying to detect. This is because while the absolute position cannot be detected, the absolute vehicle speed that serves as a reference for wheel air pressure detection cannot be detected.

Therefore, it is difficult for the above-mentioned conventional wheel air pressure detection device to secure the air pressure detection accuracy in urban areas and mountainous areas. For example, even if a wheel is punctured in a tunnel, that puncture will occur. It was something that could not be detected.

The present invention has been made in view of the above-mentioned points, and detects the ground vehicle speed based on the Doppler shift of the wave generated toward the road surface, and estimates the wheel air pressure by using the detected value as the absolute vehicle speed. It is therefore an object of the present invention to provide a wheel air pressure detection device that can solve the above problems.

[0008]

FIG. 1 is a block diagram showing the principle of a wheel air pressure detecting device for achieving the above object. That is, the above-mentioned object is to generate a wave of a predetermined frequency from the vehicle toward the road surface, to detect the Doppler shift that occurs in the reflected wave of the wave, and to detect the absolute vehicle speed of the vehicle with respect to the road surface based on the Doppler shift. Detecting means 1 and wheel speed detecting means 2a to 2d provided for each wheel of the vehicle
And an absolute vehicle speed detected by the absolute vehicle speed detecting means 1 and a wheel speed for each wheel detected by the wheel speed detecting means 2a to 2d, and an air pressure estimating means 3 for estimating an air pressure state of each wheel. It is achieved by a wheel air pressure detecting device comprising:

Further, in the wheel air pressure detecting device having such a structure, the reference wheel speed calculating means 4 for calculating a reference wheel speed based on the wheel speed of each wheel detected by the wheel speed detecting means 2a to 2d, and the above Reliability determining means for determining whether or not the detected absolute vehicle speed is an appropriate value based on the deviation between the absolute vehicle speed detected by the absolute vehicle speed detecting device 1 and the reference wheel speed calculated by the reference wheel speed calculating means 4. 5, the air pressure estimating means 3 takes in the detection value of the absolute vehicle speed detecting means 1 as an appropriate value only when the reliability determining means 5 determines that the absolute vehicle speed is appropriate. It is effective for improving the detection accuracy of air pressure.

[0010]

In the wheel air pressure detecting device according to the present invention, the absolute vehicle speed detecting means 1 emits a wave of a predetermined frequency from the vehicle toward the road surface and detects the ground vehicle speed based on the Doppler shift generated in the reflected wave of the wave. . That is, since the frequency of the wave emitted from the absolute vehicle speed detecting means 1 shows a Doppler shift according to the traveling direction of the vehicle and the vehicle speed, the ground vehicle speed is detected as the absolute vehicle speed with respect to the road surface based on the frequency change of the wave. Will be.

The air pressure estimating means 3 takes in the absolute vehicle speed thus detected and the detection values of the wheel speed detecting means 2a to 2d for detecting the rotation speeds of the respective wheels, and is ideal for the detected absolute vehicle speed. Calculate the difference between the rotation speed of and the measured rotation speed. And the rotation speed of the wheel is
The air pressure is estimated by paying attention to the fact that it varies depending on the outer diameter of the wheel, that is, the wheel air pressure.

On the other hand, the reference wheel speed calculation means 4 is a reference wheel based on the detection values of the wheel speed detection means 2a to 2d installed on the wheels predicted to be normal under high credibility. Calculate speed. Therefore, when the detected value of the absolute vehicle speed detecting means 1 is significantly different from the reference wheel speed, it can be determined that the reliability of the detected absolute vehicle speed is low.

The reliability determining means 5 determines the reliability of the absolute vehicle speed detecting means 1 by paying attention to such a point, and the deviation between the detected absolute vehicle speed and the reference wheel speed is a constant level. Only when it is within the range, it is determined that the absolute vehicle speed is a proper value. Therefore, according to the configuration in which the air pressure estimating means 3 takes in the absolute vehicle speed only when such a proper determination is made, a high detection accuracy of the wheel air pressure is always maintained.

[0014]

FIG. 2 is a conceptual diagram showing the overall construction of a wheel air pressure detecting device according to an embodiment of the present invention. In the figure, FW1 and FW2 are the left and right front wheels, respectively, and RW1 and FW1.
RW2 indicates the left and right rear wheels, respectively. Left and right front wheels FW1,
Link mechanisms 10a, 10b, 11a for connecting to FW2,
The front wheel steering device 15 is connected to the steering shaft 14 via the steering gear box 13.

On the steering shaft 14, a steering 16 is fixed, and a steering sensor 17 for detecting a steering angle is provided. The output terminal of the steering sensor 17 is a main part of the wheel air pressure detection device of the present embodiment, and is a microcomputer 18 that constitutes the air pressure estimating means 3, the reference wheel speed calculating means 4, and the reliability determining means 5. It is connected to the.

As the steering sensor 17, for example, two photocouplers and a slit plate that rotates together with the steering shaft 14 are combined to generate two sets of rectangular waves that are out of phase by π / 4 when the steering 16 rotates. Things are known.

In this case, since the four states are formed by the combination of the "high" and "low" levels of the two rectangular waves, the rotation direction of the steering wheel 16 depends on which direction the state changes. The rotation angle of the steering wheel 16 can be detected depending on how many times the state changes. Therefore, the microcomputer 18 detects the turning angles of the left and right front wheels FW1 and FW2 by monitoring the two rectangular waves emitted by the steering sensor 17, and determines whether the vehicle is going straight or turning. You can

Further, the microcomputer 18 is supplied with output signals of wheel speed sensors 19a to 19d provided for each wheel FW1, FW2, RW1, RW2.
Here, these wheel speed sensors 19a to 19d correspond to the above-mentioned wheel speed detecting means 2a to 2d, and each wheel FW1 ,.
It is a sensor that emits a pulse signal whose frequency varies according to the rotation speeds of FW2, RW1, and RW2.

Therefore, the microcomputer 18 monitors the frequencies of the signals supplied from the wheel speed sensors 19a to 19d, so that the respective wheels FW1 and FW1 during traveling are monitored.
The rotation speeds of FW2, RW1 and RW2 can be detected.

Here, the wheel air pressure detecting device according to the present embodiment has the absolute vehicle speed detecting means 1 in front of the left front wheel FW1.
It is equipped with a ground speed sensor 20 corresponding to. The ground vehicle speed sensor 20 emits a wave of a predetermined frequency to the road surface, detects the frequency of the reflected wave from the road surface, and detects the frequency of the reflected wave from the road surface. That is, it is a device for detecting the ground vehicle speed.

The configuration will be briefly described below with reference to the schematic configuration diagram of the ground vehicle speed sensor 20 shown in FIG.

The oscillator 21 shown in FIG. 3 is a transmitter that emits a wave of a predetermined frequency toward the road surface. An oscillator 22 that supplies an oscillation signal adjusted to a predetermined frequency is connected to the transmitter 21, and a wave corresponding to the oscillation signal generated by the oscillator 22 is emitted toward the road surface.

Further, as shown in FIG. 3, the transmitter 21 of the present embodiment is arranged so that waves are incident on the road surface at an elevation angle θ. Therefore, when the vehicle is traveling at the speed v, the transmitter 21 is traveling toward the road surface at a speed of vcos θ, and when the vehicle reaches the road surface, the frequency of the wave motion of the oscillator 22 due to the Doppler shift. It is higher than the emitted frequency.

The receiver 23 is arranged to receive the waves reflected irregularly on the road surface from directly above, and supplies an electric signal having a frequency corresponding to the received waves to the amplifier 24. Therefore, if the transmitter 21 emits an ultrasonic signal of frequency f and the sound velocity is V, the amplifier 24 is supplied with an electric signal of frequency f ′ represented by the following equation.

F ′ = f × V / (V−vcos θ) The frequency difference detecting circuit 25 detects the frequency difference thus generated, that is, the Doppler shift represented by “f′−f”, and It is a device that supplies the detection result to the microcomputer 18. Here, since the wave frequency f, the sound velocity V, and the elevation angle θ are known, the microcomputer 18
Can calculate the vehicle speed v back based on the Doppler shift "f'-f".

Here, the vehicle speed calculated based on the Doppler shift detected by the ground vehicle speed sensor 20 is the moving speed of the vehicle with respect to the road surface, and the wheels FW1, FW2, RW1,
This is an absolute vehicle speed that is not affected by the air pressure condition of the RW2. The absolute vehicle speed can be detected as long as an appropriate reflected wave can be obtained, and the absolute vehicle speed can be effectively operated in a wider range as compared with the conventional device that detects the absolute vehicle speed using GPS. is there.

The microcomputer 20 shown in FIG.
The ground vehicle speed sensor 20 calculates the absolute vehicle speed of the vehicle based on the Doppler shift detected in this way, and determines whether or not the wheel air pressure is normal based on the calculation result. If an abnormality is detected in any of the wheels as a result of the determination, the situation is displayed via the alarm device 26.

Hereinafter, based on the signals supplied from the ground vehicle speed sensor 20 and the wheel speed sensors 19a to 19d, the microcomputer 18 controls the wheels FW1, FW2.
A routine process of detecting the air pressures of the RW1 and RW2 and executing the alarm device 26 to warn the wheel air pressure abnormality will be described.

FIG. 4 shows a flowchart of an example of the routine executed by the microcomputer 18 as the routine process. The routine shown in the figure is a routine that is started only when it is detected from the detection signal of the steering sensor 17 that the vehicle is traveling straight ahead. Therefore,
When this routine is executed, the wheels FW1, FW2,
The wheel speeds B _FL , B _FR , B _RL , and B _RR of RW1 and RW2 should be essentially equal to the absolute vehicle speed.

When the routine shown in FIG. 4 is started, first, at step 100, it is judged if the reliability of the absolute vehicle speed is secured. When it is determined that the absolute vehicle speed is not an appropriate value as a result of testing using the method described below, considering that the absolute vehicle speed may not be accurately detected when driving on a bad road where it is difficult to obtain reflected waves from the road surface. This is because the detection result of the ground vehicle speed sensor 20 is not reflected in the estimation of the air pressure.

That is, step 100 corresponds to the reference wheel speed calculation means 4 and the reliability determination means 5 described above, and step 120 is executed only when it is determined that the reliability of the absolute vehicle speed is properly secured. The absolute vehicle speed A that is executed and calculated from the Doppler shift value detected by the ground vehicle speed sensor 20 is stored in the memory. The step 100 will be described in detail later.

After the absolute vehicle speed A is stored in the memory in this way, the routine proceeds to step 130, where each wheel speed sensor 1
Wheels FW1, FW2, RW detected by 9a to 19d
Convert the rotational speeds of 1 and RW2 into vehicle speeds, and use the values B _FL and B
Store _FR , B _RL , and B _RR in the memory as wheel speeds.

Step 140 corresponds to the above-mentioned air pressure estimating means 3, and the above-mentioned absolute vehicle speed A and wheel speed B _FL ,
Each wheel FW1, FW2, RW1, from B _FR , B _RL , B _RR
This is a step of determining whether or not the air pressure is normal for each RW2. Then, as a result of the determination, when the air pressure abnormality is detected for any of the wheels FW1, FW2, RW1, RW2, the routine proceeds to step 150, and an alarm according to the abnormal state is displayed using the alarm device 26. If no abnormality is detected, the current process is terminated.

That is, according to the wheel air pressure detecting apparatus of the present embodiment, each wheel FW is activated every time the routine shown in FIG. 4 is started.
It is determined whether or not the air pressures of 1, FW2, RW1 and RW2 are normal, and an alarm is issued as soon as the air pressure becomes abnormal.

By the way, the absolute vehicle speed A and the wheel speed B _FL ,
The wheel air pressure abnormality determination using B _FR , B _RL , and B _RR can be realized by determining whether or not the ratio of the two is near "1". Each wheel FW1, FW2, RW1, RW2
This is because the wheel speeds B _FL , B _FR , B _RL , and B _RR converted from the rotational speed should be equal to the absolute vehicle speed A if the air pressure is in an ideal state.

However, even if the air pressure is constant,
The wheel speeds B _FL , B _FR , B _RL , and B _RR are usually not microscopically constant due to changes in the loads applied to the wheels FW1, FW2, RW1, and RW2, expansion and contraction or rigidity of the suspension, and the like. Is. Therefore, the wheel speeds B _FL , B _FR ,
In the configuration in which the ratio between B _RL and B _RR and the absolute vehicle speed A is calculated and the value is compared with an appropriate judgment value, a chattering phenomenon may occur near the judgment value.

As a method of preventing such a chattering phenomenon, a method of comparing a characteristic value averaged over an appropriate period with a judgment value is generally used. Also in this embodiment, the wheel speeds B _FL , B _FR , B _RL , and B _RR calculated at each moment are calculated.
And the absolute vehicle speed A are averaged over an appropriate period,
If the configuration in which the average value is compared with the predetermined determination value is adopted, the chattering phenomenon described above can be effectively prevented.

On the other hand, the wheels FW1, FW2, RW1, RW
The modes in which the air pressure fluctuates in No. 2 include a mode in which the air pressure changes rapidly due to a puncture as shown in FIG.
There is a mode that gradually changes due to air leakage as shown in (B). In the latter mode, there is no problem in the time until the alarm is issued after the occurrence of an abnormality, but in the former case, that is, when the puncture occurs, it is necessary to promptly notify the driver of the state. Therefore, assuming such a situation, the method of averaging the ratios of the wheel speeds B _FL , B _FR , B _RL , B _RR and the absolute vehicle speed A and comparing them with the determination value is not preferable because of poor response.

Therefore, in this embodiment, as shown in FIG.
As shown in (A) and (B), a puncture determination value α that satisfies α>β>1> γ, an air pressure shortage determination value β, and an excess pressure determination value γ are set, and the calculated puncture determination value α is the calculated wheel. Speed B _FL , B
The ratio of _FR , B _RL , B _RR and the absolute vehicle speed A is used as it is, and for the shortage determination value β and the excess determination value γ, the average values of the ratios calculated at each moment are compared.

FIG. 6 is a flow chart of the air pressure abnormality determination processing executed according to this principle, and shows the details of the processing in step 140.

That is, in step 141 in FIG. 6, the wheel speeds B _FL , B _FR , B _RL , and B _{RR are} first determined on the assumption that the air pressure in each of the wheels FW1, FW2, RW1, and RW2 is to be determined.
And the absolute vehicle speed A is calculated. And step 14
2, B _FL / A, B _FR / A, B _RL / A, B _RR / A
Moving average, that is, the average value FL in the past predetermined period
H, FRH, RLH, RRH are calculated.

In this way, the wheel speeds B _FL , B _FR , B _RL ,
After calculating the ratio between B _RR and the absolute vehicle speed A, and the average value thereof, the routine proceeds to step 143, where B _FL / A, B _FR / A, B
_{The RL} / A, B _RR / A and the puncture judgment value α are compared and judged. Here, the puncture determination value α is a value sufficiently larger than the air pressure shortage determination value β as described above, and unless the air pressure is significantly reduced by the puncture, B _FL / A (or B _FR / A, B _RL / A, _BRR / A) <α holds.

On the other hand, B _FL / A, etc. is a substitute characteristic value of the wheel air pressure at each moment, so that when the air pressure is suddenly reduced due to a _flat tire, B _FL / A (or B _FR /
A, B _RL / A, B _RR / A) <α is not established. That is, the determination in step 143 is not established only when a puncture occurs on any of the wheels.

Step 144 is a moving average FLH, FR.
This is a step of comparing H, RLH, and RRH with the shortage determination value β and the excess determination value γ. Where the moving average FL
H, FRH, RLH, RRH are B _FL / A, B _FR / A,
Since B _RL / A and B _RR / A are averaged over a predetermined period, as shown in FIG. 5B, B _FL / A and B _FR /
When A, B _RL / A and B _RR / A slightly change, they are not directly affected by the change.

If the wheel air pressure is insufficient, the vehicle
B because the outer diameter of the wheel is small_FL/ A is greater than "1"
If the wheel air pressure is excessive,
B _FL/ A etc. fluctuates slightly around a value smaller than "1"
Therefore, the values of FLH, FRH, RLH, RRH are
It represents the long term condition of wheel air pressure.

Therefore, in the determination of step 144, when the wheel air pressure suddenly changes due to a puncture or the like, the effect cannot be immediately reflected, but on the other hand, the excess or deficiency of the wheel air pressure can be comparatively caused without the adverse effect of chattering. It can be judged with a narrow management range.

As described above, the wheel air pressure detecting device of the present embodiment determines the puncture that requires excellent responsiveness, and prevents the chattering while monitoring the air pressure that is required to be monitored with an appropriate control width. We will perform the shortage judgment separately,
Both demands that conflict with each other are met.

If it is determined that the conditions are satisfied in both steps 143 and 144, that is, if it is determined that the wheel air pressure is not abnormal, the routine proceeds to step 145, where the alarm output flag is reset, and then FIG. The routine shown ends. On the other hand, if the condition is not satisfied in either step 143 or 144, the process proceeds to step 146 to set the alarm output flag for the corresponding wheel, and then the alarm process is performed in step 150, and then the alarm process is performed as shown in FIG. Exit the routine.

As described above, in the apparatus of this embodiment, whether or not the air pressures of the wheels FW1, FW2, RW1 and RW2 are proper is determined on the basis of the absolute vehicle speed A detected by the ground vehicle speed sensor 20. Therefore, the air pressure can be reliably detected even in mountainous areas and urban areas, as long as the road surface can properly reflect the waves. Therefore, it is possible to secure a wider stable operation area as compared with the conventional device that detects the absolute vehicle speed by using, for example, GPS.

Even when the ground vehicle speed sensor 20 is used, there are cases where the absolute vehicle speed A cannot be properly detected while traveling on a rough road such as an unpaved road. In this case, the absolute vehicle speed A detected by the ground vehicle speed sensor 20 without any limitation.
If the abnormality determination of the air pressure is performed on the basis of, the determination accuracy naturally deteriorates.

The step 100 in FIG. 4 is a step set in view of this point, and the ground vehicle speed sensor 20
This is a step of verifying whether or not the absolute vehicle speed A calculated based on the Doppler shift of the wave detected by is appropriate.

That is, as described above, if the wheel air pressure is maintained at an appropriate level and the detection accuracy of the ground vehicle speed sensor 20 is appropriate, the wheel speeds B _FL , B _FR , B _RL , B _RR and the absolute vehicle speed are calculated. Originally becomes a constant velocity, and its frequency distribution should show a narrow normal distribution as shown by the solid line in FIG. Then, when they frequently and greatly differ from each other and a wide distribution is formed as shown by a broken line in FIG. 7,
The detection result of the ground speed sensor 20 or the wheel speeds B _FL , B
There is a problem in the detection accuracy of _FR , B _RL , and B _RR .

Here, the wheel speeds B _FL , B _FR , B _RL , and B _RR are rarely flat in all the wheels, and therefore, for example, the minimum value out of four or two from the smaller one. Or adopt the average value of 3 etc. as the standard vehicle speed,
If the reference vehicle speed and the detection result of the ground vehicle speed sensor 20 are compared, sufficient credibility for the reference vehicle speed is ensured.

Therefore, if the frequency distribution as shown in FIG. 7 is obtained in relation to the reference vehicle speed, it is possible to judge whether the detected value of the ground vehicle speed sensor 20 is proper or not depending on the width of the distribution. Is. FIG. 8 is a flowchart of the processing executed to verify the reliability of the absolute vehicle speed according to the principle, and shows the internal processing of step 100 in detail. Hereinafter, a method for verifying the reliability of the absolute vehicle speed will be described with reference to FIG.

When the routine shown in FIG. 8 is executed,
Without step 101, the wheel speed B _FL, B_FR, B_RL, B
_RRCalculate the average of 3 from the smaller one as B
It The average value B was guaranteed to be normal as described above.
This is because the reference vehicle speed is set. That is, in this routine
In addition, this step 101 is the above-mentioned reference wheel speed calculator.
Corresponds to a step. The standard vehicle speed is 3 from the smallest.
One average value, minimum value, two from the smallest, or
You can also use two averages, excluding the maximum and minimum values.
Yes.

After calculating the reference vehicle speed B in this way, the routine proceeds to step 102, where the difference "A-" between the absolute vehicle speeds A and B calculated based on the detection value of the ground vehicle speed sensor 20.
B "is calculated in order to obtain the deviation of the absolute vehicle speed A from the reference vehicle speed.

Then, in this routine, when the width of the frequency distribution is obtained based on the deviation thus obtained, the variance of the past N deviation data is calculated in step 103, that is, N "A- The cumulative value of (A−B) ² for B ″ is obtained. In this case, the absolute vehicle speed A
Is properly detected and changes following the reference vehicle speed B, the variance value becomes a small value. Conversely, if a large error is superimposed on the absolute vehicle speed A, the variance value is unreasonable. It should be a large value.

In consideration of such characteristics, step 104 compares the variance value calculated to determine the reliability of the absolute vehicle speed A with a predetermined determination value. If the variance value is smaller than the determination value, the normal value and the variance value are determined. When the value is equal to or larger than the judgment value, it is a step of judging as abnormal. That is, this step 10
4 implements the reliability determination means 5 described above together with the above steps 102 and 103.

If it is judged to be normal in step 104, step 105 is executed. If it is judged to be abnormal in step 104, step 106 is executed.
At, the reliability OK or NG flag is set for each absolute vehicle speed A, and thereafter the routine shown in FIG. 4 is continuously executed.

That is, if the reliability of the absolute vehicle speed A is judged to be OK, the above-mentioned processing from step 120 is continuously executed, and if the reliability is NG, step 1 is executed.
The _routine proceeds to step 10, where the minimum value of the wheel speeds B _FL , B _FR , B _RL , and B _RR is stored as the absolute vehicle speed A, and the processing after step 130 is executed with reference to such A.

Here, the minimum value is used as A:
This is because it can be predicted that the vehicle is in a normal state with high credibility because the influence of punctures and air leakage is estimated to be the smallest, and the wheel speed B is the same as in the case of the reference vehicle speed described above. _In addition to selecting the minimum value of _FL , B _FR , B _RL , and B _RR , it is also possible to use the average value of two or three from the smaller one, or the two average values excluding the maximum and minimum values. .

By performing such processing, when the absolute vehicle speed sensor 20 cannot detect the proper absolute vehicle speed while traveling on a bad road, the air pressure detection is continued with the absolute vehicle speed with a large error as a reference. Therefore, the air pressure can be detected while maintaining appropriate accuracy at all times.

In the case of mainly improving the detection accuracy of the wheel air pressure, when the reliability of the absolute vehicle speed is judged to be NG, the wheel air pressure detection processing is not executed thereafter and the process shown in FIG.
A configuration for terminating the routine shown in may be adopted. That is, the reliability of the absolute vehicle speed becomes NG mainly when traveling on a bad road such as an unpaved road, and the wheels FW1 and F
W2, RW1 and RW2 tend to idle, and wheel speed B _FL ,
Since B _FR , B _RL , and B _RR are unlikely to be the substitute characteristic values of the wheel air pressure, the wheel air pressure detection accuracy may deteriorate.

In this case, in the structure for monitoring the reliability of the absolute vehicle speed as described above, the wheels FW1, FW2, RW
It is possible to estimate whether or not the RW1 and RW2 are in a state of being easily slipped from the determination result of the reliability of the absolute vehicle speed, and stop the detection when it is determined to be unsuitable for the detection of the air pressure. By doing so, it is possible to improve the detection accuracy as a whole.

Although the wheel air pressure detecting apparatus of this embodiment employs a configuration in which the processing for judging the reliability of the absolute vehicle speed is always executed, the present invention is not limited to this, and the detection by the ground vehicle speed sensor 20 is not limited to this. Such processing can be omitted depending on the accuracy and the accuracy required for wheel air pressure detection.

Further, the ground vehicle speed sensor 20 of this embodiment is
Although an ultrasonic wave is used as the wave of a predetermined frequency, any wave capable of detecting the Doppler shift is sufficient, and for example, an electromagnetic wave or the like can be used.

[0067]

As described above, according to the first aspect of the present invention, the accuracy is determined by determining whether the wheel speed of each wheel is an appropriate value with reference to the ground vehicle speed detected by the absolute vehicle speed detecting means. In addition to being able to detect the wheel air pressure well, the absolute vehicle speed does not become undetectable in mountainous areas, urban areas with many high-rise buildings, etc., unlike the conventional device that detects absolute vehicle speed using GPS, and it is wide. It has the feature that detection of wheel air pressure can be performed in a range.

According to the second aspect of the present invention, the absolute vehicle speed detecting means detects the wheel speed of one of the wheels mounted on the vehicle, which is guaranteed to be normal under high credibility. Since the detection result of the absolute vehicle speed detecting means is used for estimating the air pressure only when the reliability of the result is judged and sufficient reliability is ensured, it is more comprehensive than the invention according to claim 1. The accuracy of accurate air pressure detection is improved.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of a wheel air pressure detection device according to the present invention.

FIG. 2 is an overall configuration diagram of a wheel air pressure detection device that is an embodiment of the present invention.

FIG. 3 is a block configuration diagram of a ground vehicle speed sensor which is a main part of the wheel air pressure detection device of the present embodiment.

FIG. 4 is a flowchart of an example of a wheel air pressure detection routine executed by a microcomputer of the wheel air pressure detection device of this embodiment.

FIG. 5 is a diagram for explaining a method for determining wheel air pressure in the present embodiment.

FIG. 6 is a flowchart of an example of wheel air pressure abnormality determination processing executed by the microcomputer of the wheel air pressure detection device according to the present embodiment.

FIG. 7 is a diagram showing a relationship between detection accuracy of a ground vehicle speed sensor and frequency distribution.

FIG. 8 is a flowchart of an example of absolute vehicle speed reliability determination processing executed by the microcomputer of the wheel air pressure detection device according to the present embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Absolute vehicle speed detection means 2a-2d Wheel speed detection means 3 Air pressure estimation means 4 Reference wheel speed calculation means 5 Reliability determination means FW1, FW2 Front wheels RW1, RW2 Rear wheels 17 Steering sensor 18 Microcomputer 19a-19d Wheel speed sensor 20 Ground Vehicle speed sensor 26 Alarm device

Claims (2)

[Claims] 1. An absolute vehicle speed detection for emitting a wave of a predetermined frequency from a vehicle to a road surface, detecting a Doppler shift generated in a reflected wave of the wave, and detecting an absolute vehicle speed of the vehicle with respect to the road surface based on the Doppler shift. Means, a wheel speed detecting means provided for each wheel of the vehicle, an absolute vehicle speed detected by the absolute vehicle speed detecting means, and a wheel speed for each wheel detected by the wheel speed detecting means are compared,
A wheel air pressure detecting device comprising: an air pressure estimating means for estimating an air pressure state of each wheel. 2. The wheel air pressure detection device according to claim 1, wherein reference wheel speed calculation means calculates a reference wheel speed based on the wheel speed of each wheel detected by the wheel speed detection means, and the absolute vehicle speed. Based on a deviation between the absolute vehicle speed detected by the detection device and the reference wheel speed calculated by the reference wheel speed calculation means, a reliability determination means for determining whether the detected absolute vehicle speed is a proper value is provided, The wheel air pressure detecting device, wherein the air pressure estimating means takes in the detection value of the absolute vehicle speed detecting means as an appropriate value only when the reliability determining means determines that the absolute vehicle speed is appropriate.